title: Effect of isomeric structures of branched cyclic hydrocarbons on densities and equation of state predictions at elevated temperatures and pressures.
abstract: The cis and trans conformation of a branched cyclic hydrocarbon affects the packing and, hence, the density, exhibited by that compound. Reported here are density data for branched cyclohexane (C6) compounds including methylcyclohexane, ethylcyclohexane (ethylcC6), cis-1,2-dimethylcyclohexane (cis-1,2), cis-1,4-dimethylcyclohexane (cis-1,4), and trans-1,4-dimethylcyclohexane (trans-1,4) determined at temperatures up to 525 K and pressures up to 275 MPa. Of the four branched C6 isomers, cis-1,2 exhibits the largest densities and the smallest densities are exhibited by trans-1,4. The densities are modeled with the Peng-Robinson (PR) equation of state (EoS), the high-temperature, high-pressure, volume-translated (HTHP VT) PREoS, and the perturbed chain, statistical associating fluid theory (PC-SAFT) EoS. Model calculations highlight the capability of these equations to account for the different densities observed for the four isomers investigated in this study. The HTHP VT-PREoS provides modest improvements over the PREoS, but neither cubic EoS is capable of accounting for the effect of isomer structural differences on the observed densities. The PC-SAFT EoS, with pure component parameters from the literature or from a group contribution method, provides improved density predictions relative to those obtained with the PREoS or HTHP VT-PREoS. However, the PC-SAFT EoS, with either set of parameters, also cannot fully account for the effect of the C6 isomer structure on the resultant density.
authors.affiliation: National Energy Technology Laboratory, Office of Research and Development, Department of Energy, Pittsburgh, Pennsylvania 15236, USA. wuy@vcu.edu
authors.forename: Yue
authors.initials: Y
authors.lastname: Wu
authors.forename: Babatunde A
authors.initials: BA
authors.lastname: Bamgbade
authors.forename: Ward A
authors.initials: WA
authors.lastname: Burgess
authors.forename: Deepak
authors.initials: D
authors.lastname: Tapriyal
authors.forename: Hseen O
authors.initials: HO
authors.lastname: Baled
authors.forename: Robert M
authors.initials: RM
authors.lastname: Enick
authors.forename: Mark A
authors.initials: MA
authors.lastname: McHugh